The present invention relates to a flame retardant (FR) halogen-free aromatic polycarbonate (PC) composition.
Many applications require that a polycarbonate composition be flame retardant and combine ease of processing with good optical properties. Typically, flame retardancy is obtained through the use of additives, which are halogen or heavy metal-containing compositions that may form toxic materials when heated. There is an increasing awareness of the effects of these materials and increasing demand for polycarbonate compositions that do not contain potentially toxic flame retardant additives.
Siloxane additives are known to enhance flame retardant properties of polycarbonate compositions. Compression molded {fraction (1/16)} inch bars of polycarbonate compositions with siloxane additives that have condensed triorganosiloxy units can pass the UL94 test with VO rating. See xe2x80x9cFlammability of Plastic Materials Bulletinxe2x80x9d of Jan. 24, 1980. Aromatic polyester siloxane-containing polycarbonate compositions also exhibit flame retardant properties. However, these polycarbonate compositions can be difficult to process due to incompatibility of the siloxane additive with the polycarbonate.
There is a need for a flame retardant additive for polycarbonate compositions that is sufficiently flame-retardant to obtain a satisfactory UL94 rating, that does not form toxic materials, that imparts good flow as measured by a satisfactory high melt flow index value, that does not affect optical properties, and that improves processibility. Particularly, there is a need for a flame retardant polycarbonate composition that meets UL94 requirements for VO rating at {fraction (1/16)} inch thickness. Additionally, there is a need for fabrication materials that will emit low smoke and heat when burning.
The present invention provides a polycarbonate composition comprising components (A) and (B) wherein component (A) comprises a polycarbonate and component (B) comprises a silsesquioxane.
The present invention further provides a method of making a flame retardant composition comprising providing a polycarbonate and incorporating a flame retardant amount of a silsesquioxane into the polycarbonate.
As used hereinafter, the term xe2x80x9cflame retardantxe2x80x9d means reduced or eliminated in tendency to ignite when exposed to a low-energy flame. The term xe2x80x9cUL94 V0xe2x80x9d when used in conjunction with xe2x80x9cflame retardantxe2x80x9d means that a described polycarbonate composition can satisfy the UL94 requirements for VO flammability, as described in the xe2x80x9cFlammability of Plastic Materials Bulletinxe2x80x9d of Jan. 24, 1980. In this test, a 5 inch by xc2xd inch by {fraction (1/16)} inch polycarbonate test bar containing an amount of a flame retardant additive is suspended vertically over a xc2xe inch Bunsen Burner flame. A material meets requirements for a UL94 V0 rating when a test bar satisfies the following 5 tests: (1) a test bar of the material does not burn with flaming combustion for more than 10 seconds after application of a test flame, (2) no set of five test bars exhibits a total flaming combustion time exceeding 50 seconds for 10 flame applications, (3) no test bar of the material burns with flaming or glowing combustion up to the holding clamp, (4) no test bar drips flaming particles that ignite dry absorbent surgical cotton located 12 inches (305 millimeters) below the bar, and (5) no test bar exhibits glowing combustion that persists for more than 30 seconds after twice applying and removing the test flame.
The polycarbonate composition of the invention contains a silsesquioxane elastomer resin. Silsesquioxanes are siloxanes of the formula R(SiO3/2)n wherein n equals an even number higher than or equal to 4, for example 4, 6, 8, etc. and R is independently at each occurrence phenyl, C1-C8 alkyl, cycloalkyl, vinyl, or combinations of the same. The silsesquioxanes are cage-like hybrid molecules of silicon and oxygen with similarities to both silica and silicone. When mixed with virtually any ordinary polymer, they bond to the organic molecules and to one another, forming large chains that weave through the polymer. The result may be a nanostructured organic-inorganic hybrid polymer.
The SiO3/2 units are assembled into spherical, highly symmetric cage-compounds. Terminal R units are not incorporated into the silicate framework. These structural characteristics led to the name spherosiloxanes. The spherosiloxane class of silsesquioxane shows a broad variety. Many different terminal substituents (organic and inorganic, e.g., R=alkyl, aryl, hydroxy, chlorine) are known. The SiO3/2 unit is synthetically accessible to n in a range between about 4 and about 18. Suitable silsesquioxane elastomer resins in the invention include silsesquioxanes of the following formula (I): 
wherein R is independently at each occurrence the same or different moiety selected form the group consisting of phenyl, C1-C8 alkyl, cycloalkyl, vinyl, and combinations thereof. Preferably, R is selected from phenyl, vinyl, methyl, and combinations thereof. The silsesquioxane in the present invention is typically made via copolymerization of phenylsilsesquioxane with dimethylsiloxane to form a (phenyl-silsesquioxane)-co-(dimethyl siloxane) of the general formula, TPhxDy wherein D has the formula (CH3)2SiO2/2, T has the formula (C6H5)SiO3/2, subscript x is in a range between about 0.1 and about 1, and subscript y is in a range between about 0.1 and about 1. A further example of a silsesquioxane in the present invention is a poly(phenyl vinyl silsesquioxane) of the general formula (RSiO3/2)x(RSiO3/2)y(RSiO3/2)z where R is independently at each occurrence phenyl, C1-C8 alkyl, cycloalkyl, and vinyl; and x+y+z is the total degree of polymerization of the resin. These and related materials are prepared by hydrolysis condensation of either RSiCl3 or RSi(ORxe2x80x2)3. For example, if a 9:1 mole ratio of (C6H5)SiCl3 and vinylSiCl3 are hydrolyzed and condensed, then a poly ((C6H5)SiO3/2)0.9x(vinylSiO3/2)0.1x resin is obtained.
Among the polycarbonates that can be rendered flame retardant in the practice of the present invention are included aromatic polycarbonates formed, for example, by phosgenating the following bisphenols: p,pxe2x80x2-bisphenol A, m,p-bisphenol A, o,p-bisphenol A, spirobindane bisphenol, tetramethylbisphenol A and tetramethylbiphenol. Copolycarbonates containing the aforementioned bisphenols as a major bisphenol constituent are also included. Preferably, the aromatic polycarbonate is a bisphenol A polycarbonate having an intrinsic viscosity (IV) in a range between about 0.35 deciliters per gram (dl/g) and about 1.8 dl/g in chloroform at 25xc2x0 C.
Aromatic polycarbonate resins are, in general, prepared by reacting a dihydric phenol with a carbonate precursor or a carbonate ester. Suitable dihydric phenols for preparing polyestercarbonates include those represented by the formula XII:
HOxe2x80x94Dxe2x80x94OHxe2x80x83xe2x80x83(XII)
wherein D is a divalent aromatic radical. Preferably, D has the structure of formula XIII; 
wherein A represents an aromatic group such as phenylene, biphenylene, naphthylene, etc.; and E may be an alkylene or alkylidene group such as methylene, ethylene, ethylidene, propylene, propylidene, isopropylidene, butylene, butylidene, isobutylidene, amylene, amylidene, isoamylidene, etc. Where E is an alkylene or alkylidene group, it may also consist of two or more alkylene or alkylidene groups connected by a moiety different from alkylene or alkylidene, such as an aromatic linkage; a tertiary amino linkage; an ether linkage; a carbonyl linkage; a silicon-containing linkage; or a sulfur-containing linkage such as sulfide, sulfoxide, sulfone, etc.; or a phosphorus-containing linkage such as phosphinyl, phosphonyl, etc. In addition, E may be a cycloaliphatic group (e.g., cyclopentylidene, cyclohexylidene, 3,3,5-trimethylcyclohexylidene, methylcyclohexylidene, 2-[2.2.1]-bicycloheptylidene, neopentylidene, cyclopentadecylidene, cyclododecylidene, adamantylidene, etc.); a sulfur-containing linkage, such as sulfide, sulfoxide or sulfone; a phosphorus-containing linkage, such as phosphinyl, phosphonyl; an ether linkage; a carbonyl group; a tertiary nitrogen group; or a silicon-containing linkage such as silane or siloxy. R16 represents hydrogen or a monovalent hydrocarbon group such as alkyl, aryl, aralkyl, alkaryl, or cycloalkyl. Y1 may be an inorganic atom such as halogen (fluorine, bromine, chlorine, iodine); an inorganic group such as nitro; an organic group such as R16 above, or an oxy group such as OR; it being only necessary that Y1 be inert to and unaffected by the reactants and reaction conditions used to prepare the polyestercarbonate. The letter m represents any integer from and including zero through the number of positions on A1 available for substitution; p represents an integer from and including zero through the number of positions on E available for substitution; t represents an integer equal to at least one; s is either zero or one; and u represents any integer including zero.
In the dihydric phenol compound in which D is represented by formula XIII above, when more than one Y substituent is present, they may be the same or different. The same holds true for the R16 substituent. Where s is zero in formula XIII and u is not zero, the aromatic rings are directly joined with no intervening alkylidene or other bridge. The positions of the hydroxyl groups and Y1 on the aromatic nuclear residues A1 can be varied in the ortho, meta, or para positions and the groupings can be in vicinal, asymmetrical or symmetrical relationship, where two or more ring carbon atoms of the hydrocarbon residue are substituted with Y1 and hydroxyl groups.
Some illustrative, non-limiting examples of dihydric phenols of formula XII include the dihydroxy-substituted aromatic hydrocarbons disclosed by name or formula (generic or specific) in U.S. Pat. No. 4,217,438. Some preferred examples of dihydric phenols include 4,4xe2x80x2-(3,3,5-trimethylcyclohexylidene)diphenol; 2,2-bis(4-hydroxyphenyl)propane (commonly known as bisphenol-A); 2,2-bis(4-hydroxy-3,5-dimethylphenyl)propane; 2,4xe2x80x2-dihyroxydiphenylmethane; bis(2-hydroxyphenyl)methane; bis(4-hydroxy-phenyl)methane; bis(4-hydroxy-5-nitrophenyl)methane; bis(4-hydroxy-2,6-dimethyl-3-methoxyphenyl)methane; 1,1-bis(4-hydroxyphenyl)ethane; 1,1-bis(4-hydroxy-2-chlorophenyl)ethane; 2,2-bis(3-phenyl-4-hydroxyphenyl)-propane; bis(4-hydroxyphenyl)cyclohexylmethane; 2,2-bis(4-hydroxyphenyl)-1-phenylpropane; resorcinol; and C1-3 alkyl-substituted resorcinols.
Suitable dihydric phenols also include those containing spirobiindane structural units such as represented by the formula XIV: 
wherein each R17 is independently selected from monovalent hydrocarbon radicals and halogen radicals; each R18, R19, R20, and R21 is independently C1-6 alkyl; each R22 and R23 is independently H or C1-6 alkyl; and each n is independently selected from positive integers having a value in a range between about 0 and about 3 inclusive. The monovalent hydrocarbon radicals represented by R17 include alkyl radicals, cycloalkyl radicals, aryl radicals, aralkyl radicals, and alkaryl radicals. Alkyl radicals represented by R17 are preferably those containing carbon atoms in a range between about 1 and about 12, and include branched alkyl radicals and straight chain alkyl radicals. Some illustrative non-limiting examples of these alkyl radicals include methyl, ethyl, propyl, isopropyl, butyl, tertiary-butyl, pentyl, neopentyl, and hexyl. Cycloalkyl radicals represented by R17 are preferably those containing ring carbon atoms in a range between about 3 and about 12. Some illustrative non-limiting examples of these cycloalkyl radicals include cyclobutyl, cyclopentyl, cyclohexyl, methylcyclohexyl, cycloheptyl. Aryl radicals represented by R17 are preferably those containing ring carbon atoms in a range between about 6 and about 12. Some illustrative non-limiting examples of these aryl radicals include phenyl, biphenyl, and naphthyl. Preferred aralkyl and alkaryl radicals represented by R17 are those containing carbon atoms in a range between about 7 and about 14. These include, but are not limited to, benzyl, ethylphenyl, phenylbutyl, phenylpropyl, propylphenyl, and phenylethyl. The preferred halogen radicals represented by R17 are fluorine, chlorine and bromine.
In the dihydric phenol compound of formula XIV when more than one R17 substituent is present they may be the same or different. The relative positions of the hydroxyl groups and R17 on the aromatic nuclear residues may be varied in the ortho or meta positions. The position of each hydroxy group is independently at any unsubstituted site on each of the aromatic rings. More preferably, each hydroxy group is independently in positions 5 or 6 and 5xe2x80x2 or 6xe2x80x2 of each aromatic ring. Most preferably, each hydroxy group is in position 6 and 6xe2x80x2 of each aromatic ring.
Preferably, each R17 is independently selected from chlorine, bromine, and lower alkyl radicals containing carbon atoms in a range between about 1 and about 5, each R18, R19, R20, and R21 is independently C1-6 alkyl; each R22 and R23 is independently H or C1-6 alkyl; and each n is independently in a range between about 0 and about 3. More preferably, each R17 is independently selected from chlorine and lower alkyl radicals containing carbon atoms in a range between about 1 and about 3, each R18, R19, R20, and R21 is independently C1-2 alkyl; each R22 and R23 is independently H or C1-2 alkyl; and each n is independently in a range between about 0 and about 2. Still more preferably, each R18, R19, R20, and R21 is methyl; each R22 and R23 is H; and each n is 0.
The Spiro dihydric phenols of formula XIV are compounds that are known in the art and are commercially available or may be readily prepared by known methods. Methods of preparation include, for example, those described in U.S. Pat. No. 4,701,566; and by R. F. Curtis and K. O. Lewis in Journal of the Chemical Society (England), 1962, p. 420; and by R. F. Curtis in Journal of the Chemical Society (England), 1962, p. 417. In one illustrative, non-limiting example, these spiro dihydric phenols may be conveniently prepared by (i) reacting two moles of a phenolic compound with one mole of a carbonyl-containing compound such as acetone, and (ii) thereafter co-reacting 3 moles of the product of (i) under acidic conditions to form the spiro dihydric phenol and 4 moles of a phenolic compound. The acids which may be utilized in (ii) can include such acids as anhydrous methane sulfonic acid, anhydrous hydrochloric acid, and the like.
The most preferred spiro dihydric phenol for forming polyestercarbonates suitable for use in the present invention is 6,6xe2x80x2-hydroxy-3,3,3xe2x80x2,3xe2x80x2-tetramethyl-1,1xe2x80x2-spirobiindane (xe2x80x9cSBIxe2x80x9d), in which n in formula XIV is 0 and the linkages with the rest of the polymer molecule are in a specific position on the aromatic rings.
In the preparation of suitable polyestercarbonates, the dihydric phenols described above may be used alone or as mixtures of two or more different dihydric phenols. For reasons of availability and particular suitability for the purposes of this invention, a preferred dihydric phenol is 2,2-bis(4-hydroxyphenyl)propane (bisphenol-A or xe2x80x9cBPAxe2x80x9d), in which D in formula XII is bis(4-phenyl)isopropylidene.
Examples of carbonate precursors include, but are not limited to, a carbonyl bromide of a dihydric phenol, a carbonyl chloride of a dihydric phenol, a halogen formate of a dihydric phenol, and a bishaloformate of a dihydric phenol. Examples of carbonate esters include, but are not limited to, diphenyl carbonate, dichlorophenyl carbonate, dinaphthyl carbonate, phenyl tolyl carbonate and ditolyl carbonate.
In a preferred embodiment of the present invention, the aromatic polycarbonate resin comprises one or more resins selected from linear aromatic polycarbonate resins, branched aromatic polycarbonate resins, and poly(estercarbonate) resins. Suitable linear aromatic polycarbonates resins include, but are not limited to, bisphenol A polycarbonate resins. Suitable branched aromatic polycarbonates are made, for example, by reacting a polyfunctional aromatic compound with a dihydric phenol and a carbonate precursor to form a branched polymer. Examples of polyfunctional aromatic compounds include, but are not limited to, trimellitic anhydride, trimellitic acid, trimesic acid, trihydroxy phenyl ethane, and trimellityl trichloride. Suitable poly(estercarbonate) copolymers are made, for example, by reacting a difunctional carboxylic acid such as terephthalic acid, isophthalic acid, 2,6-naphthalic acid, dodecanedioic acid, or mixtures of acids, or a derivative of a difunctional carboxylic acid such as an acid chloride, with a dihydric phenol and a carbonate precursor.
In a preferred embodiment of the present invention, the polycarbonate resin has an intrinsic viscosity in a range between about 0.3 deciliters per gram and about 1.5 deciliters per gram in methylene chloride at 25xc2x0 C. In a preferred embodiment of the present invention, the polycarbonate resin is a linear polycarbonate resin that is derived from bisphenol A and phosgene. In an alternative preferred embodiment of the present invention, the polycarbonate resin is a blend of two or more polycarbonate resins. When the polycarbonate resin is a blend of two or more polycarbonate resins, the at least two resins may be different because of different monomer content, or the at least two resins may have similar monomer content but be different, for example, because of different molecular weights.
Suitable aromatic polycarbonate resins are commercially available, e.g., LEXAN(copyright) bisphenol A-type polycarbonate resins which are produced by General Electric Company.
The silsesquioxane can be intimately mixed with the polycarbonate by compounding in a mixing apparatus such as a Banbury mixer, twin screw extruder, or the like to form a uniform dispersion of the polycarbonate and silsesquioxane.
The amount of flame retardant silsesquioxane should be present in an amount at least sufficient to reduce the flammability of the polycarbonate, preferably to a UL94 V0 rating. The amount will vary, for example, with the nature of the polycarbonate and with the efficiency of the flame retardant silsesquioxane additive. In general, however, the amount of flame retardant silsesquioxane additive is in a range between about 0.1 percent by weight and about 20 percent by weight, desirably in a range between about 0.25 percent by weight and about 10 percent by weight, and preferably in a range between about 0.5 percent by weight and about 3 percent by weight based on the weight of polycarbonate.
The compositions can include the flame retardant silsesquioxane with an additive such as at least one of an anti-drip agent, synergist, stabilizer, impact modifier, or filler. The flame retardant polycarbonate composition can be reinforced with inert fillers such as silica filler, carbon fibers, or glass fibers. The proportion of filler can vary in a range between about 1 part and about 100 parts of filler per 100 parts by weight of the resulting polycarbonate composition. The reinforcing material is typically a glass fiber reinforcing agent, mineral filler, talc, clay, mica, silica, milled glass, flaked glass, or carbon fibers. Preferably, glass fiber or filamentous glass is employed as a reinforcement in the present compositions. For compositions to be employed for electrical uses, it is preferred to use fibrous glass filaments comprising borosilicate glass that is relatively soda-free. This is known as xe2x80x9cExe2x80x9d glass. The filaments are made by standard processes, e.g., by steam or air blowing, flame blowing and mechanical pulling. The preferred filaments for plastic reinforcement are typically made by mechanical pulling. The filament diameters are preferably in a range between about 3 microns and about 30 microns. In preparing a molding composition, it is convenient to use the filamentous glass in the form of chopped strands in a range between about xe2x85x9 inch and about xc2xd inch long.
In other embodiments of the present invention, the composition can include an impact modifier. Particularly useful impact modifiers generally include rubbery impact modifiers. These are well known to those skilled in the art, and any of them normally employed with polyester resins may be employed herein. A preferred impact modifier comprises an acrylic or methacrylic grafted polymer of a conjugated diene or an acrylate elastomer, alone or copolymerized with a vinyl aromatic compound. Particularly useful are core-shell polymers of the type available from Rohm and Haas, for example, those sold under the trade designation Acryloid(copyright) (Rohm and Haas Company, Philadelphia, Pa.). In general these impact modifiers contain units derived from butadiene or isoprene, alone or in combination with a vinyl aromatic compound, or butyl acrylate, alone or in combination with a vinyl aromatic compound. Most preferably, the impact modifier will comprise a two stage polymer having either a butadiene or butyl acrylate based rubbery core grafted to a shell composed of polymethyl methacrylate and a second stage polymerized from methylmethacrylate alone, or in combination with styrene. Also present in the first stage are cross linking monomers, graft linking monomers, or combinations thereof. Examples of the crosslinking monomers include, but are not limited to, 1,3-butylene diacrylate, divinyl benzene and butylene dimethacrylate. Examples of graftlinking monomers include, but are not limited to, allyl acrylate, allyl methacrylate and diallyl maleate. Another preferred impact modifier includes a relatively high content of a butadiene polymer grafted base having grafted thereon acrylonitrile and styrene. Other suitable impact modifiers include, but are not limited to, ethylene vinyl acetate, ethylene ethylacrylate copolymers, SEBS (styrene-ethylene-butylene styrene) and SBS (styrene-butadiene-styrene) block copolymers, EPDM (ethylene propylene diene monomer) and EPR (ethylene propylene rubber) copolymers, etc.
The polycarbonate composition can contain a stabilizer. Typically, such stabilizers are used at a level in a range between about 0.01 weight percent and about 10 weight percent and preferably, at a level in a range between about 0.05 weight percent and about 2 weight percent based on the weight of the polycarbonate. The preferred stabilizers include, but are not limited to, one or more of phosphorus oxo acids, an acidic phosphate salt, an acid phosphite, an alkyl phosphite, an aryl phosphite, or a mixed phosphite having at least one hydrogen or alkyl group. The suitability of a particular compound for use as a stabilizer and the determination of how much is to be used as a stabilizer may be readily determined by preparing a mixture of the polycarbonate with and without the particular compound and determining the effect on melt viscosity or color stability. The acidic phosphate salts include, but are not limited to, sodium dihydrogen phosphate, mono zinc phosphate, potassium hydrogen phosphate, calcium hydrogen phosphate and the like. The phosphate can be a salt of a Group IB or Group IIB metal such as zinc phosphate, copper phosphate, and the like. The phosphorus oxo acids include, but are not limited to, phosphorous acid, phosphoric acid, polyphosphoric acid, hypophosphorous acid, or combinations thereof.
In one embodiment of the present invention, the polycarbonate composition is free from halogen additive or heavy metal-containing additive. However in another embodiment of the present invention, the polycarbonate composition can include an adjunct flame retardant ingredient, which in some instances may be a halogenated aromatic flame-retardant. Such retardants include, but are not limited to, tetrabromobisphenol A polycarbonate oligomer, polybromophenyl ether, brominated polystyrene, brominated BPA polyepoxide, brominated imides, brominated polycarbonate, poly(haloaryl acrylate), poly(haloaryl methacrylate) or mixtures thereof. Poly(haloaryl acrylates) are preferred with the most preferred being poly(pentabromobenzyl acrylate).
Examples of other suitable adjunct flame retardants are brominated polystyrenes such as polydibromostyrene and polytribromostyrene; decabromobiphenyl ethane; tetrabromobiphenyl; brominated alpha, omega-alkylene-bis-phthalimides, for example, N,Nxe2x80x2-thylene-bis-tetrabromophthalimide; oligomeric brominated carbonates, especially carbonates derived from tetrabromobisphenol A, which may be end-capped with phenoxy groups, brominated phenoxy groups, or brominated epoxy resins. Other examples aromatic carbonate flame retardants are set forth in U.S. Pat. No. 4,636,544 to Hepp. The adjunct flame retardant ingredient may be present in a range between about 10% by weight and about 20% by weight based on the weight percent of polycarbonate resin in the final composition.
A silsesquioxane flame retardant can be used with a synergist such as an inorganic antimony compound. Typical synergists include, but are not limited to, antimony pentoxide (Sb2O5); antimony sulfide (SbS3) and the like. An especially preferred synergist is antimony oxide (Sb2O3). The synergist is typically used in a range between about 0.5 percent by weight and about 15 percent by weight, and more preferably in a range between about 1 percent by weight and about 6 percent by weight based on the weight percent of polycarbonate resin in the final composition.
Also, the final composition may contain polytetrafluoroethylene (PTFE) type resins or copolymers used to reduce dripping in flame retardant thermoplastics. The PTFE type resins or copolymers are typically present in a range between about 0.01% by weight and about 1% by weight based on the total composition, and more typically, in a range between about 0.2% by weight and about 0.5% by weight based on the total composition. Preferably ingredients such as stabilizers, mold release, lubricants, colorants, nucleants, antioxidants and UV absorbers are employed in low amounts, typically less than 5 percent by weight of the total composition.
Articles which are molded from the flame retardant polycarbonate composition, especially injection molded enclosures, are suitable for use in electrical communication devices such as cable connections, telephone, computer, video, etc. and network interface devices for residential, commercial and industrial use and in aircraft and skyscraper fabrication.